When used as a noun, it is one word.
London has many historic landmarks.
When used as a verb, it is two words.
The sailor's discovery of land marks the end of his voyage.
I can only think of one. Which is the Belize Barrier Reef.
one of the landmarks are the Great Wall
the amber museum is one of the landmarks
Interesting
It is used as one word.
no it is not an one word it is of two word
I think the word "ongoing" is only one word, but it has two syllables that are two separate words.
Hipbone is one word.
The word "hairbrush" is typically written as one word, not two.
One word, two syllables
It is one word.
one word